Focal seizures are created in monkeys, at birth and at pubescence, by injecting 25,000 units of penicillin into the right face-hand area of the cerebral motor cortex. The development and propagation of the seizures is monitored by electroencephalography, electromyography and clinical observations. At selected increments of the propagation the animal is decapitated, the head frozen and the active subcortical neuronal aggregates are delineated by an increase in the regional cerebral glucose utilization as determined by the (14C) deoxyglucose method.